我有一个 Angular 应用程序以及使用 SignalR 的 ASP.NET Core 2.2 后端。启动连接时，我收到错误：
Error: Failed to complete negotiation with the server: Error
Error: Failed to start the connection: Error
点击 localhost:5000/chatHub- 时的响应标头
HTTP/1.1 204 No Content
Date: Tue, 19 Feb 2019 08:52:52 GMT
Server: Kestrel
Access-Control-Allow-Headers: x-requested-with
Access-Control-Allow-Methods: POST
Access-Control-Allow-Origin: *
Startup.cs-
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using RealChat.Hubs;
namespace RealChat
{
public class Startup …